I'm so glad to have this story!! It's a sweet TF story written by  Zephyr10101 of Leon transforming to his Lynel self after getting a Lynel mask from a mysterious shop owner
I hope you enjoy the read!

************************************************
Horns of Lynel
By: Zefurr
“I can’t believe Halloween is only a few days away” a young woman said hopping onto the sidewalk. She was trailed by two of her friends, both of them coming back from the gym while she, from work.
“Yeah, it’s crazy how fast the year has went by” the young man coming up next to her said.
“Hey Leon, we still on for games later? I gotta go home and change” he said to the blonde haired young man. The boy in question fixed his glasses and adjusted the gym bag on his shoulder.
“Yeah sure Chris, I have to shower and stuff anyway. By the way, have you guys gotten your costumes for Caitlin’s party yet? I totally forgot” he asked them. Chris groaned and face palmed his forehead.
“Hell, I forgot all about that thing. What about you Miranda?” he said nudging the young woman next to him.
“Sorry boys, some of us are proactive” she said winking at them. “I finished my costume weeks ago.”
Chris snorted at her. “Guess being a perfectionist fashion major helps huh?”
She narrowed her eyes at him. “You bet your ass it does. I didn’t spend all those sleepless nights just to sew for the rest of my life.”
Chris continued to laugh and provoke their friend and bicker. Meanwhile, Leon was lost in thought wondering what he should wear to the costume party. Knowing Caitlin, he’d have to go all out since her parties are always over the top.
“Leon!” Chris said bringing out of his thoughts. He friend slung an arm over his shoulder grinning at some idea he cooked up.
“Since you and me don’t have costumes yet, I was thinking tomorrow we can go costume hunting.”
Miranda rolled her eyes. “This late into the Halloween season? You two will be lucky to find costume ears around here.”
“Aw, ye a little faith Miranda, I’m sure there’s still something around here.” Leon laughed at his friends.
“I’m with her on this one dude. It’s even too late to order anything online I bet.”
Chris pouted. “Aw come onnnnnn man. Pleeease? I’ll be your best buddy”
“I thought you were my best buddy.”
“Yeah but now I’ll be even better than that” he persisted. “Besides, you know how Caitlin gets. If everything isn’t perfect we’ll catch the coldest of shoulders and pay later on.”
Leon shuddered at the last time they dropped the ball on a Caitlin related event. He still remembers the ice burns.
“Okay fine, we’ll go costume shopping tomorrow then” Leon conceded.
Chris’ eyes lit up. “Sweet! I’ll just spend the night then haha.”
Miranda shook her head at the two of them. They got to her house and she waved goodbye to them.
“I’ll see you guys at the party on Saturday. Don’t be late~” she said and closed her door.
Luckily they all lived relatively close to one another. Miranda was by the gym where Leon’ car was parked. He loaded his stuff in and got in the car with Chris following.
***
That evening, the boys played a variety of video games cycling through various gaming systems.
“Well, this game really is worth all the hype” Chris started.
“Right!? It’s an awesome Zelda game” Leon said excitedly. Breath of the wild was currently his favorite in the series. “Gliding, climbing whatever the heck you want, tons of eye candy, and taming the horses.”
“How crazy was that last shrine dude?” Chris told him taking another handful of popcorn. Leon almost flailed his hands in frustration just remembering.
“It was insane! That damn labyrinth with that storm? Was cool that it gave a lot of cool stuff though.” Chris nodded at that.
“Was worth the hell we had to go through with those guardians. Luckily, we knew to shield before being weegee’d to death.” Leon spit out his soda at that laughing.
“The barbarian headdress item is pretty awesome. Gonna add to the randomness of my character’s outfit.”
Leon looks over at the time yawning. “It’s getting pretty late, we should call it a night. Gotta get up tomorrow to go ‘Halloween shopping’ right?”
Chris punched his shoulder. “Smartass, but yeah we should head to bed.” He said packing up his switch. Leon turned off the living room and lights and headed for the stairs to his room.
“Night man” he called down.
“Night dude” Chris said settling in on the couch.
***
“Ugh that was the third costume place. It’s like a tornado of wannabe cosplayers came through here” Chris said slumping against a brick wall.
Leon sat down next to him and shrugged. “Well, it is like Halloween in 2 days so what’d you expect?”
“A lot more than this at least. Even the lame costume are gone!”
Leon laughed. “Well I guess we know better for next year right? Ready to call it a quits?”
Chris stood up dusting himself off. “Screw that, we’re gonna find something. Just gotta find the right shop.”
Leon sighed. “Dude, we’ve been at this for hours. I’m pretty sure we’ve hit every costume place around town. No one has anything. Face it, we’re 50 shades of screwed over.”
Chris narrowed his eyes at his friend. “With that defeatist attitude we are. Where the heck are we anyway?” he said looking around.
“Ummm downtown somewhere? I’ve never been to this part of town though. Everything’s kinda run down or old” Leon said looking at the old buildings.
Some of them have seen better days. They looked to be still usable but others looked half destroyed. Mold and graffiti littered the places around them. Not many people were around either.
“Internet says this used to be the old downtown before all that renovation. The city just kinda left this place to rot” Chris stated reading his phone.
“Knowing the mayor, she’ll bulldoze this district for some fancy apartments no one in this small town needs anyway.” Leon said continuing to walk along the old, cracked sidewalk. Chris followed after him.
“Who knows? Maybe we’ll get a new mall or something.”
“Yes, cause that’s just what this place needs” Leon laughed.
The two kept walking along the sidewalk for a few more blocks. Leon was about ready to call it a quits again and go back home. Caitlin could just do whatever unspeakable things she wanted.
Chris pulled his out of his thoughts stopping him mid step with a hand to his chest. “Whoa dude, look at that!” he said pointing to an old, slightly decrepit building. The sign outside read ‘All Hallows Eve Wardrobe’.
“Dude, this is it. Come on” he said pulling Leon towards the place.
“Is this place even open? It looks super old.”
“And probably has the coolest costumes too.”
The boys walked up on the wooden porch to the shop which creaked under their weight.
“Is this place even open?” Chris said peeking through the window. Just then, the door flew open shocking them both. Chris turned tail to leave.
“Nah man, I’m out” Chris said before Leon grabbed his arm.
“Oh hell no, you dragged me all across this city all day. We’re going in” he said pushing his friends towards the door.
Once inside, they could see how old yet modern the inside was. It smelled like closed-up room. Costumes were all around the store. There were racks of clothes, shelves of items, and display cases full of trinkets and masks.
Leon and Chris walked around the shop looking at all the stuff. “Wow, some of these costumes are surprising up to date given the…décor” Chris said motioning to the outside.
“Can I help you gentlemen?” a voice said making Chris jump and Leon shout.
The man behind them laughed. He was older, could be about their parent’s age in his 40s. He was tall, had short white hair and sideburns wearing a grey buttoned shirt and slacks.
“I’m sorry. I didn’t mean to scare you boys” he said apologetically.
“It’s fine” Leon began. “The door just flew open and we didn’t know if anyone was here or not.”
“Ah yes, I must get that old thing fixed. But please, feel free to browse. We don’t get many visitors these days after the renovations.”
“A lot of these costumes are really well made mister….” Leon trailed off.
“Norman. Call me Norman” he said offering his hands. Both Leon and Chris shook it introducing themselves.
The boys browsed around the costume shop more at ease now. Chris found a realistic Dracula costume he liked and ended up buying it. Chris came across a display case with the coolest thing he saw.
“Is this..is this a lynel mask from Legend of Zelda?” he called out to Mr. Norman who was behind the counter at the register.
The man smiled a wicked smile not lost on Chris who raised an eyebrow.
“Ah yes, yes. One of my best creations. Hand made with some love.. and a touch of magic” he said winking and chuckling.
Chris didn’t pick up on the creepiness too mesmerized by the mask. He picked it up and observed it up closed. It reminded him of a Japanese oni mask. It had the horns and everything. Lion-like face with a scar across the left eye and a bit of a white and black mane behind the face mask part.
“I’ll take it!” Leon said excitedly.
“Excellent choice” the shop keeper smiled.
***
Leon kept the mask in its case all that day until it was time for the party. Caitlin rented out a local park for the evening’s festivities. There were tents around and caterers serving food. The part seemed to be in full swing, music playing distantly in the background.
The rest of Leon’s outfit was in the back he brought with him. An authentic looking barbarian’s vest and pants to go with his faux weapon.
He was going to change in the bathroom to not ruin it beforehand. Chris and Miranda were already there mingling. Some were saying how Chris was acting a little bit “too” into character.
Leon took the mask out its case and exited his car. He put it on heading for the park bathroom when he felt his entire body rumbling and he struggled to stay uptight and fell to his knees. He felt as if the ground was shaking underneath him.
He grabbed his head in pain unsure to what’s suddenly come over him. The hands holding his head were quickly darkening. The skin turning greyer before settling on a dark grey. The same grey was trailing down his body. He felt little pinpricks along his skin that was fur growing out. The grey fur turned whiter on the backs of his elbows where it grew out thicker than the rest.
His nails were lengthening and sharpening into claws. He grit his teeth that were also becoming sharper. The seam of the mask once visible was disappearing more and more before no trace of it could be found on his skin. Leon’s forehead hurt as it felt like something was drilling
into his head. In actuality, the horns from the mask were fusing and becoming a part of his head. They grew out taller and curved slightly before the change stopped on his head.
Once blue eyes opened back up to reveal glowing red ones. Leon felt his mouth and nose stretch out to join the empty space between the mask and his changing face. Soon he could smell and see through the nose and eyes of it as if it were his own.
Leon’s hair also was growing out at an astonishing rate. His once blonde hair was becoming lighter and lighter going from bleach blonde to pure white. The grey hair from the mask mixed in with his new mane forming grey streaks along it. So much of it grew down his back tangling into messy braids.
The young man felt the rumbling start up again in his lower body and fell onto his butt. He watched as his clothes ripped. Shirt straining where new muscles were forming. His upper body and abdomen becoming more defined. His pants were torn to shreds as his leg muscles expanded. Leon felt an uncomfortable pressure in his feet that bubbled until he felt relief when his shoes popped off. What he saw was not his feet however. He saw hooves. Black hooves with fur trailing up his ankles where his feet should be. The fur was thick around his new hooves. It reminded Leon of a Clydesdale horse.
He felt a slight a slight discomfort feeling the joints in his new legs pop and his leg bend inwards. That subsided however once he felt a pain in how lower abdomen. He lifted his the remnants of his shirt revealing two new appendages growing out at a fast rate above his thick navel hair. They were the same color as his normal skin before they started darkening and growing fur to match his new form. The growth forced him to stand although the position awkward.
This changed once he felt his legs start to grow further and further away from his body. He was confused for a second looking behind him to see how much larger his lower body has becoming. His new front hooves supporting him as the hair grew thick around his ankles. He felt his tailbone, or at least that’s what it felt like, start to move away from his spine. Growing out inch by inch before the flesh was covered in the same hair color as his mane.
Leon thought the changes were finally over til his saw parts of his body lightening to a luminescent white in striped patterns across his new body. The changes stopped along his new tail.
“Incredible!” he boomed in a much deeper voice. He stumbled a bit trying to use his new legs but worked up a trot to join the other party guests shocking them all with his realistic his “costume” was. Caitlin pouted being outdone at his own party.
Norman watched from the trees of the park nearby laughing to himself. “Two more satisfied customers.”
END